Flow Through in-Line Micro Pin Fin Arrays With Variable Spacings

Flow behaviors of water through in-line micro pin fin arrays with different longitudinal spacings (2–4 times the diameter of pin fin) are visually investigated. Streamline patterns and velocity distributions in the Reynolds number range of 100–800 were obtained by microscale particle image velocimetry. Vortex evolution, and the effects of longitudinal spacing on vortex structure and velocity distribution were analyzed. Additionally, the results were compared with those in the staggered micro pin fin arrays and used to explain the resistance characteristics. The investigation revealed that the longitudinal spacing hinders vortex development and delays the occurrence of vortex shedding in the in-line configurations with the longitudinal spacing lower than 3 times the diameter of pin fin. Larger longitudinal spacing yields a more uniform velocity field in in-line micro pin fin arrays. Extension of vortex is identified as a key factor contributing to increased flow resistance after the steady vortex appearance. Furthermore, flow through the in-line micro pin fin array exhibits shorter actual flow distance, lack of transverse velocity, and a smaller effectively convective area compared with the staggered micro pin fin array, which may account for the distinct resistance characteristics and heat transfer performance in the in-line arrangement.